1. Field of the Invention
The present invention relates to an image forming apparatus such as a color electrographic printer (referred to below as a color printer).
2. Description of the Related Art
There is a color printer that forms monochromatic toner images of different colors on surfaces of photosensitive drums using LED (Light Emitting Diode) heads in a plurality of image forming units and while conveying a recording paper by a belt, sequentially transfers the toner images from the surfaces of the respective photosensitive drums onto a surface of the recording paper in a superposed manner.
In the color printer, depending on processing accuracy of unit parts, mounting accuracy of the LED heads, or other factors, a line of each of the toner images formed by the image forming units may be independently inclined. In such a case, when the toner images are sequentially transferred and superposed on the surface of the recording paper, color shift occurs among the toner images.
Thus, the color printer forms predetermined detection patterns by the image forming units, transfers them onto the belt surface, detects reflection intensities of the detection patterns through a reflection intensity detection unit, and detects the inclination of a line in each toner image based on the detection results. Then, in formation of a print image, the color printer corrects the inclinations of lines in the toner images on the surfaces of the photosensitive drums by controlling the LED heads in accordance with the detected inclinations, thereby preventing color shift from occurring among the toner images transferred on the recording paper (for example, see Japanese Patent Application Publication No. 2001-134041).
Further, there is a color printer of intermediate transfer type, which sequentially transfers toner images formed by image forming units onto a surface of a belt in a superposed manner and then transfers the toner images from the surface of the belt onto a surface of a recording paper.
In the color printer of intermediate transfer type, the belt is stretched by a roller and may be partially distorted. As a result, different amounts of distortion may occur in the toner images on the surface of the belt. This may cause a color shift among the toner images on the belt surface, resulting in deterioration of a print image.